We have characterized the pattern of expression of the main markers of epithelial differentiation, namely keratins, involucrin and cross-linked evelopes, in human epithelia derived from these major cancer sites during the course of terminal differentiation in embryonic development, in postnatal maturation, and/or in neoplasia. The pattern of expression was found to be dependent on the cell type, the stage of differentiation and/or development and the extrinsic environment of the cell. Distinctive qualitative and quantitative differences in the spectrum of keratin proteins were found in the carcinomas compared with their nontransformed counterparts. Moreover, assessment of cross-linked envelope-forming capabilities or for the presences of involucrin served as specific markers for squamous and urothelial differentiation; the extent of involucrin staining or envelope formation correlated well with the degree of squamous differentation in both normal epithelia and tumors. We have established human esophageal and lung carcinoma cell lines in cell culture and compared the growth and differentiated properties of these carcinoma cells with their nontransformed counterparts. Significant changes in the array of keratins and in the proportions of cell making cross-linked evelopes were noted. The results we obtained paralleled findings with tumor masses indicating that the tumor cells in cell culture continue to maintain a program of gene expresion reflective of that of the original tumor.